Exposure apparatus and a device manfacturing method using the same

ABSTRACT

A scanning type exposure apparatus includes a projection optical system which projects a pattern of a reticle onto a wafer, which is held by a wafer chuck, a scanning stage system which scanningly moves the reticle and the wafer synchronously with respect the projection optical system, and an inspection system which automatically inspects influence of particles on at least one of the wafer and on the wafer chuck. The inspection system includes a focus detector which measures a focus state of the wafer and a calculator which calculates outputs of the focus detector.

This application is a continuation application of copending patentapplication Ser. No. 11/114,158 filed Apr. 26, 2005 which is adivisional of patent application Ser. No. 10/207,768, filed on Jul. 31,2002 which issued as U.S. Pat. No. 6,897,949 on May 24, 2005, and whichis a continuation of patent application Ser. No. 09/418,253, filed onOct. 15, 1999, which issued as U.S. Pat. No. 6,456,374 on Sep. 24, 2002.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a scanning type exposure apparatus andmethod, and a device manufacturing method, wherein the exposureapparatus is preferably used in a lithography process for manufacturingmicro-devices.

2. Description of the Related Art

In a lithography process of micro-device (semiconductor) manufacturing,two types of exposure apparatuses are known. One is a step-and-repeattype (so-called a stepper) and the other is a step-and-scan type(so-called a scanner or a scanning type exposure apparatus).

The former type uses a step-and-repeat sequence for transferringstepwise a pattern of an original (e.g., a reticle or a mask) onto asubstrate (e.g., a semiconductor wafer or a glass substrate). In thatsequence, the whole pattern of the original is illuminated and isprojected onto one of a plurality of exposure regions of the substratethrough a projection optical system, while the original and thesubstrate are maintained stationary. Next, the substrate is movedstepwise to change the exposure region and then exposure is repeated inthe same manner.

On the other hand, the latter type uses a step-and-scan sequence. Inthat sequence, the original pattern is illuminated with a slit-like beamand a portion of the pattern is projected onto one of the exposureregions of the substrate, while both the original and the substrate arescanningly moved. Then, the substrate is moved stepwise to change theexposure region, and thereafter the exposure is repeated in the samemanner.

The latter step-and-scan type exposure apparatus seems to have becomethe mainstream, expected at least in the near future, for the reasonthat it has a high potential of exposure performance in terms of anincrease in transferring precision and field size.

The scanning type exposure apparatus mainly comprises stage devices(e.g., a wafer stage or a reticle stage) for scanningly moving the waferand the reticle (mask), an illumination optical system and a projectionoptical system. In this apparatus, while scanning exposure is performed,the wafer stage and the reticle stage are synchronously controlled by amaster-slave control method, in which the wafer stage is a master stageand the reticle stage is a slave stage, and the reticle stage followsthe movement of the wafer stage in the scanning direction. Themaster-slave control method provides an advantage in improving movementresolution, especially when the projection optical system is a reducedscale system.

The apparatus also includes detection systems, e.g., laserinterferometers for detecting the stage positions in the scanningdirection, and a focus detector for detecting a distance between thewafer surface and a focal plane of a projection optical system duringthe scanning exposure, for adjusting the wafer surface with respect to afocal plane of the projection optical system.

Time series outputs from the focus detector tend to have smoothvariations. With the recent advancements in wafer planarizationprocesses and to increase pattern transfer accuracy, wafers areprocessed to be as smooth as possible. As a result, the focus detectionoutputs typically do not have sudden variations, at least within eachchip area (shot area).

Conversely, adjusting the wafer surface in the tilt direction accordingto a detection having sudden variations causes defocusing within thechip area. For example, if a 50 ppm inclination was obtained as thefocus detection on a condition that the chip area has a 20 mm size in alongitudinal slit direction, there exists 50 ppm×20 mm=1 micron ofheight difference in a Z direction between edge portions of the chiparea. Since the recent exposure apparatuses have a DOF (Depth Of Focus)of at most 0.7 micron, it is difficult to perform exposure withoutcausing any defocusing in each of the chip areas.

One of the expected causes of sudden focus detection variations is thepresence of contaminated particles on the wafer or the wafer chucksurface. For example, wafer resist exfoliation particles are apt tocling onto the wafer surface or the chuck surface in the form of suchcontaminated particles. Semiconductor manufacturing processes pay closeattention to reduce such resist exfoliation particles, and regularmaintenance checks are performed to replace and clean the wafer chuck.However, the contaminated particles on the chuck are frequently notdetected. Therefore, the chuck may become contaminated during the termbetween the maintenance checks. Consequently, productivity (e.g., chipproduction yield) deteriorates.

SUMMARY OF THE INVENTION

It is an object of the invention to provide an improved exposureapparatus and a semiconductor manufacturing method having highreliability and productivity.

According to one aspect of the present invention, a scanning typeexposure apparatus comprises a projection optical system which projectsa pattern of a reticle onto a wafer, which is held by a wafer chuck, ascanning stage system which scanningly moves the reticle and the wafersynchronously with respect the projection optical system, and aninspection system which automatically inspects influence of particles onat least one of the wafer and on the wafer chuck.

According to another aspect of the present invention, an inspectionmethod for a scanning type exposure apparatus comprises the steps ofholding a wafer on a chuck of a wafer stage, scanningly moving, by thewafer stage, the held wafer relative to a focus detector, detecting, bythe focus detector, a focus state of the wafer a plurality of times in arow while scanning is performed, and producing a plurality of detectiondata, and comparing the plurality of detection data to a threshold, inorder to determine sudden changes of the plurality of data.

According to yet another aspect of the present invention, a devicemanufacturing method for manufacturing micro-devices comprises the stepsof holding a wafer on a chuck of a wafer stage, holding a reticle havinga pattern on a reticle stage, scanningly moving the reticle and thewafer synchronously with respect a projection optical system and a focusdetector, so as to transfer the pattern onto the wafer, detecting, bythe focus detector, a focus state of the wafer a plurality of times in arow while scanning is performed, and producing a plurality of detectiondata, and comparing the plurality of detection data to a threshold inorder to determine sudden changes of the plurality of data.

These and other objects, features and advantages of the presentinvention will become more apparent from the following description ofthe preferred embodiments taken in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a scanning type exposure apparatusaccording to the invention.

FIG. 2 is a schematic view of a system for detecting particles in theexposure apparatus of FIG. 1.

FIG. 3A is a flowchart of a method for inspecting particles in each chiparea and FIG. 3B shows information stored in a memory storing step ofthe FIG. 3A flowchart.

FIG. 4 is a flowchart showing a process for manufacturing amicro-device.

FIG. 5 is a flowchart showing the detailed steps of the wafer process inthe micro-device manufacturing process shown in FIG. 4.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention will be described in further detail by way of example withreference to the accompanying drawings.

FIG. 1 schematically illustrates a scanning type exposure apparatus formanufacturing semiconductors according to an embodiment of the presentinvention. Referring to FIG. 1, the apparatus comprises a light source10, such as an excimer laser (e.g., KrF, ArF or F₂), an illuminationoptical system 11, a reticle stage 12, which holds and moves a reticle13 having a device pattern, a projection optical system 14, and a waferstage 15, which holds and moves a wafer 16 to be exposed. Theillumination optical system 11 reshapes the light beam from the lightsource 10 to form a slit beam having a width of several millimeters. Theslit beam illuminates the reticle 13 held by the reticle stage 12. Theprojection optical system 14 projects a portion of the reticle patternonto the wafer 16 at a desired reduction magnification, e.g., 4:1 or5:1.

The apparatus further comprises laser interferometers 17, 18, whichrespectively measure the position of the reticle stage 12 and the waferstage 15 in the scanning direction (Y-direction), and a focus detector19, which detects a distance (Z-direction) and an inclination(tilt-directions) between the wafer surface and a focal plane of theprojection optical system 14. The focus detector 19 comprises an obliqueincidence detection system, having a light source and a photodetector,which illuminates the wafer 16 with an oblique light beam by the lightsource and detects a focusing state or a position of the reflected lightby the photodetector. In another embodiment, the focus detector mayinclude a fluid micrometer system, which applies a pressurized gastoward the wafer and detects a back pressure of the gas.

While scanning exposure is performed, movement of the reticle stage 12and the wafer stage 15 is synchronously controlled using a master-slavecontrol method, based on the measurements of the interferometers 17, 18.Thereby, a larger exposure field can be obtained. Also, the focus in theZ-direction and the leveling in the tilt-directions of the wafer stagecan be controlled based on the measurement of the focus detector 19.

FIG. 2 illustrates a schematic view of a system for detecting particlesin the above-mentioned exposure apparatus. Referring to FIG. 2, thewafer stage 15, including a wafer chuck 20, which attracts and holds thewafer 16, can move and position the wafer 16 with six degrees offreedom. The focus detector 19 measures a distance between the focalplane of the projection optical system 14 and the upper surface of thewafer 16. A controller 5, for controlling operations of the exposureapparatus, includes a stage controller 6 and a calculator 7. Thecalculator 7 stores a computer program for automatically inspecting theinfluence of particles on at least one of the wafer and the chuck (i.e.,between the wafer chuck surface and the opposite side of the wafer). Anoperational console 8 is a user interface for the operator.

FIG. 3 is a flowchart for explaining a method of determining particleswithin each chip area processed by the controller 5. Following aninitial start-up step, the method includes the following steps. Step 1includes starting a scanning exposure operation in one chip areaaccording to the order of the controller 5. Step 2 includesinitialization, N=0. Step 3 includes performing a first time focusdetection. Step 4 includes storing measured data in perpendiculardirections, Z, Wx and Wy, in a memory. Measurement positions in the chiparea have been previously set in the controller 5. In step 5, N isincremented by one to N=N+1. In step 6, the detection returns to step 3,M (>1) times, while scanning is performed, for M>N. The plurality ofdetection data obtained in a row are stored in a matrix in the memory,as shown in FIG. 3B. Scanning exposure is completed in step 7.

In step 8, after the scanning exposure is finished, the calculator 7calculates differences between measured values of an N(1˜M−1)thdetection and an (N+1)th detection. In step 9, a calculated differenceis compared with a threshold. In step 10, if no calculated differenceexceeds a threshold (predetermined value), then operation proceeds tothe end. However, if any calculated difference exceeds a threshold, thatmeans a sudden change of values has occurred and it is determined instep 11 that at least one particle could exist on or near the measuredposition on the wafer 16 or on the holding surface of the wafer chuck20.

In step 12, the operational console 8 displays a message or sounds awarning signal to indicate to the operator that a potential particleexists, based on the calculation. Therefore, it is possible to abort anexposure operation based on an instruction of the operator, orautomatically, in order to clean the wafer chuck 16 for removing theparticles. Hence, it is easy to reduce defective chips and to increasemanufacturing productivity.

Meanwhile, although the above example shows a method of performing thefocus detection during the pattern transfer for detecting particles,another solution could be provided. That is, the apparatus can have aspecial inspection mode to detect particles without performing patterntransfer, namely, by performing the focus detection while moving thewafer stages without illuminating the reticle and the wafer withexposure light.

Further, it may be desirable to modify the above embodiment intodetermining particles for every wafer (including a plurality of chipareas), instead of for each chip area. That would be achieved bymemorizing the measured data of all chip areas of the wafer andperforming calculations for every wafer at the time of waferreplacement. Also, it is possible to analyze historical data for eachwafer, for example, by comparing the Nth and the (N+1)th wafer. Such anarrangement is illustrated in the flow chart of FIG. 6 wherein the Nthwafer is processed in accordance with the flow chart of FIG. 3A in step601 and the Nth+1 wafer is then processed in accordance with the flowchart of FIG. 3A in step 605. After the processing in steps 601 and 605,positions of the M positions of each of the Nth and Nth+1 wafers areselected in steps 610 and 615 and the measured values of the selectedpositions of the Nth and Nth+1 wafers are compared in the step 620.Historical data for the compared positions is displayed in step 625.

FIG. 4 is a flowchart showing a process for manufacturing a micro-device(e.g., a semiconductor chip such as an IC or an LSI, a liquid crystalpanel, a CCD (charge-coupled device), a thin film magnetic head, amicro-machine or the like). At step 1 (circuit design), the circuitdesign of the semiconductor device is effected. At step 2 (themanufacturing of a mask), a mask (reticle) formed with the designedcircuit pattern is manufactured. At step 3 (the manufacturing of awafer), a wafer is manufactured by the use of a material such assilicon. Step 4 (wafer process) is called a pre-process, in which by theuse of the manufactured mask and wafer, an actual circuit is formed onthe wafer by lithography techniques. The next step, step 5 (assembling),is called a post-process, which is a process for making the wafermanufactured at step 4 into a semiconductor chip, and includes stepssuch as an assembling step (dicing and bonding) and a packaging step(enclosing the chip). At step 6 (inspection), inspections such as anoperation-confirming test and a durability test of the semiconductordevice manufactured at step 5 are carried out. Via such steps, thesemiconductor device is completed, and it is delivered (step 7).

FIG. 5 is a flowchart showing the detailed steps of the wafer processdiscussed above with respect to step 4. At step 11 (oxidation), thesurface of the wafer is oxidized. At step 12 (CVD), an insulating filmis formed on the surface of the wafer. At step 13 (the forming of anelectrode), an electrode is formed on the wafer by vapor deposition. Atstep 14 (ion implantation), ions are implanted into the wafer. At step15 (resist processing), a photoresist is applied to the wafer. At step16 (exposure), the circuit pattern of the mask is printed and exposedonto the wafer by the exposure apparatus. At step 17 (development), theexposed wafer is developed. At step 18 (etching), the portions otherthan the developed resist image are scraped off. At step 19 (thepeeling-off of the resist), the resist, which has become unnecessaryafter the etching, is removed. By repetitively carrying out these steps,circuit patterns are multiplexly formed on the wafer. If themanufacturing method of the present embodiment is used, it will bepossible to manufacture semiconductor devices having a high degree ofintegration, which have heretofore been difficult to manufacture.

Except as otherwise disclosed herein, the various components shown inoutline or in block form in the figures are individually well known andtheir internal construction and operation are not critical either to themaking or using of this invention or to a description of the best modeof the invention.

While the present invention has been described with respect to what isat present considered to be the preferred embodiments, it is to beunderstood that the invention is not limited to the disclosedembodiments. To the contrary, the invention is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims. The scope of the following claims is to beaccorded the broadest interpretation so as to encompass all suchmodifications and equivalent structures and functions.

1-15. (canceled)
 16. An exposure apparatus for performing an exposure ofa wafer to light via a mask while the mask and the wafer are scanned,said apparatus comprising: a projection optical system configured toproject a pattern of the mask onto the wafer; a detection systemconfigured to detect a position of a surface of the wafer in a directionof an optical axis of said projection optical system, with respect toeach of a plurality of positions on the surface arranged along adirection of a scan of the wafer, while the scan is performed; a waferstage configured to hold the wafer and to be moved based on positions ofthe surface detected by said detection system while the exposure isperformed; and a controller configured to calculate a difference and tocompare the difference with a threshold, the difference being adifference between two detected positions of a plurality of detectedpositions of the surface obtained by said detection system, the twodetected positions being obtained with respect to two successivepositions of the plurality of positions on the surface.
 17. An exposureapparatus according to claim 16, further comprising a user interfaceconfigured to perform indication concerning comparison performed by saidcontroller.
 18. An exposure apparatus according to claim 16, whereinsaid controller is configured to abort an operation of said apparatus ifthe difference exceeds the threshold.
 19. An exposure apparatusaccording to claim 16, wherein said detection system is configured tooutput information of the position of the surface, the informationincluding information of a tilt amount of the surface.
 20. An exposureapparatus according to claim 16, wherein said detection system isconfigured to detect the position of the surface optically.
 21. Anexposure apparatus according to claim 16, wherein said detection systemincludes a fluid micrometer and is configured to detect the position ofthe surface using said fluid micrometer.
 22. An exposure apparatusaccording to claim 16, wherein said controller is configured to controloperation of said detection system and said wafer stage withoutperforming the exposure.
 23. An exposure apparatus according to claim16, wherein said controller is configured to compare the difference withthe threshold with respect to each part of the wafer.
 24. An exposureapparatus according to claim 16, wherein said controller is configuredto compare the difference with the threshold with respect to each of aplurality of the wafer.
 25. An exposure apparatus for performing anexposure of a wafer to light via a mask while the mask and the wafer arescanned, said apparatus comprising: a projection optical systemconfigured to project a pattern of the mask onto the wafer; a detectionsystem configured to detect a position of a surface of the wafer in adirection of an optical axis of said projection optical system, withrespect to each of a plurality of positions on the surface arrangedalong a direction of a scan of the wafer, while the scan is performed; awafer stage configured to hold the wafer and to be moved based onpositions of the surface detected by said detection system while theexposure is performed; and a controller configured to compare a firstposition of a surface of a first wafer obtained by said detection systemwith a second position of a surface of a second wafer different from thefirst wafter, the second position being previously obtained by saiddetection system while the scan of the second wafer was previouslyperformed.
 26. A method of manufacturing a device using an exposureapparatus for performing an exposure of a wafer to light via a mask anda projection optical system configured to project a pattern of the maskonto the wafer, while the mask and the wafer are scanned, said methodcomprising steps of: detecting a position of a surface of the wafer in adirection of an optical axis of the projection optical system, withrespect to each of a plurality of positions on the surface arrangedalong a direction of a scan of the wafer, while the scan is performed;moving the wafer based on positions of the surface detected in saiddetecting step while the exposure is performed; exposing the wafer,moved in said moving step, to light via the mask and the projectionoptical system; calculating a difference, the difference being adifference between two detected positions of a plurality of detectedpositions of the surface obtained in said detecting step, the twodetected positions being obtained with respect to two successivepositions of the plurality of positions on the surface; comparing thedifference with a threshold; and performing indication concerningcomparison performed in said comparing step.
 27. A method ofmanufacturing a device using an exposure apparatus for performing anexposure of a wafer to light via a mask and a projection optical systemconfigured to project a pattern of the mask onto the wafer, while themask and the wafer are scanned, said method comprising steps of:detecting, using a detection system, a position of a surface of a firstwafer in a direction of an optical axis of the projection opticalsystem, with respect to each of a plurality of positions on the surfacearranged along a direction of a scan of the first wafer, while the scanis performed; moving the first wafer based on positions of the surfacedetected in said detecting step while the exposure is performed; andexposing the first wafer, moved in said moving step, to light via themask and the projection optical system; comparing a first position ofthe surface of the first wafer obtained in said detecting step with asecond position of a surface of a second wafer different than the firstwafer, the second position being previously obtained using the detectionsystem while the scan of the second wafer was previously performed; andperforming indication concerning comparison performed in said comparingstep.